Monday, September 8, 2008

Seawater Greenhouses (cont'd)


Photo © (top) Marc Alex/PIG/AFP,Paris: A growth industry. But at what cost ? Greenhouses near Puebla de Vilar near Almeria (Spain)

Most people think that the Great Wall of China is the only man-made structure that is visible from outer space. That is not entirely true. The roofs of tens of thousands of closely-packed plastic greenhouses in Almería province, Spain form a blanket of mirrored light that beams into space making Almeria one of the most recognizable spots on a satellite map.

From space, the reflection from the plastic shimmers and glows like the agricultural gold it has become. Almería once was a desert so dry, arid, and dusty that it was used to provide the background for spaghetti westerns. However; transparent plastic, chemical fertilizers, and new boreholes drilled into the pre-existing aquifer system mixed with a little technology has transformed Almería into Europe’s winter market garden consuming some 135 square miles.

The fresh produce grown year round was the main goal of erecting the greenhouses and their complimentary systems; but, the trickle-down benefits have made the local farmers very prosperous. Farmers wear gold jewellery; new shopping malls grow bigger than the greenhouses; seed and farming equipment replace cars and banks on billboards; immigrants come from other countries to work there – a total change of lifestyle for the residents.

Antonio Moreno, one of thousands of small holders who have contributed to this plastic jungle, stands in his 45C (113F) greenhouse and says, “You really should wear shorts in here.”

Mr. Moreno's plants will never touch soil - they grow from bags filled with oven-puffed grains of white perlite stone. Chemical fertilizers are drip-fed to each plant from four large, computer-controlled vats in a nearby room.

Every day hundreds of trucks leave Almeria taking produce directly to supermarkets in Germany, Scandinavia or Britain producing fresh fruits and vegetable to those who might otherwise not have access to them.

So, what’s not working here?

The aquifer system in Spain has been around for centuries. Until fairly recently, they were a renewable resource being renewed every year by the cold, clear, clean mountain run-off. The aquifer system used to be able to support the needs of the people; but, now with the added demand of the greenhouses, the levels of the aquifers are being lowered thus allowing seawater to enter the underground system. This increases the salinity of the water in the aquifers and makes the water increasingly unusable.

Unfortunately, there is a second problem with the aquifers. Runoff from the chemicals used to fertilize the produce is finding its way in the system. Residents in that region now drink bottled water as water from the tap is now undrinkable.

Spain is not the only greenhouse system to have gone wrong. What does the Sahara Forest Project have that the others didn’t?

Backwards logic!!

The Sahara Forest Project is working on the theory that there is no shortage of water in the world – it’s just in the wrong place and it’s too salty. They say that converting seawater to freshwater, in the right places, has the potential to solve this problem.

Seawater greenhouses have already been built in some of the hottest regions on earth, Abu Dhabi and Oman for example, where they create freshwater from seawater while providing cooler and more humid growing conditions which enable crop growing year round.

Concentrated solar power is one of the most promising forms of renewable energy producing electricity from sunlight at a fraction of the cost of photovoltaic. Less than 1% of the world’s deserts, if covered with concentrating solar power plants, could produce enough electricity to meet the world’s needs today. Imagine 1% of the world’s surface providing 100% of the world’s electricity.

By combining these technologies there is huge commercial potential to restore forests and create a sustainable source of fresh water, food and energy. The scheme is proposed at a significant scale such that very large quantities of seawater are evaporated. As every person with even a smattering of physics knows “what goes up, must come down.”

A 10,000 hectare area of seawater greenhouses will evaporate a million tonnes of seawater a day. Every single drop of evaporated seawater will fall as rainwater somewhere. If the scheme were located upwind of higher terrain; then, the air carrying this ‘lost’ humidity would be forced to rise and cool, contributing additional water to the mist or cloud.



Illustration of greenhouses having a similar effect on the climate as a region of forest, yet providing a net input of water vapor from the sea.

By using a location that lies below sea level, seawater pumping costs may be eliminated. There are a number of large inland depressions in Egypt, Libya, Tunisia and Eritrea for example. In each case, the prevailing wind direction is from the sea to the mountain areas inland.
This would eliminate all dependence on the aquifers that lay hidden beneath the sand.

Currently there are some 200,000 hectares of conventional greenhouses in Mediterranean region. As we have seen from the first part of this article many, if not all, face water quality and availability issues while contributing to contribute to the depletion of ground water. By using greenhouses to create freshwater from seawater, the problem is reversed.

1 comment:

kathi said...

- wow - what a view in Spain...

BTW, the videos dissappeared...